Regionalized perinatal health care in the United States began in the 1970s with a joint statement of recommendation from the American College of Obstetricians and Gynecologists, American Academy of Pediatrics, American Academy of Family Physicians and the American Medical Association in an effort to lower neonatal mortality rates. A system of formal networks identifying subspecialty centers for perinatal and neonatal care was designed to channel those pregnancies at risk of delivering infants with special care needs to these hospitals. The literature has demonstrated improved outcome for high-risk neonates such as those with low birthweight (LBW) born at subspecialty (level III) centers. The recent trend towards deregionalization has resulted in a greater number of LBW deliveries at level I and II hospitals. The alleged causes of this trend include the changing health care environment, and specifically, the growth of managed care. There is little existing literature demonstrating a significant association between managed care and the site of delivery for high-risk neonates. The goal of this study is to determine the extent to which deregionalization persists, and whether an association exists between managed care penetration and the site of LBW deliveries. The study will also address the role of increasing numbers of neonatal and perinatal specialists on the site of LBW deliveries. This will be accomplished by analyzing four states at four different points in time spanning 1985 to 1998. Analysis will be performed at the hospital level, with data derived from birth certificates, AHA Annual Survey results, and Area Resource Files. The primary outcome variable will be the percentage of deliveries per hospital that are LBW. Analyses will also be conducted using subgroups of LBW neonates (weighing 1500- 2500 grams, 1000-1500 grams, and 500-1000 grams). Analyses will be conducted using multiple linear regression, modified for use with panel data. Findings from the study will document current trends, and provide evidence for the impact of market forces, in particular, managed care, on the regionalization of perinatal health care in the United States.